The invention pertains to a method of estimating the temperature of the tip of a glow plug and particularly relates to the acquisition, by a simple method, of an estimated temperature of the tip of a glow plug used in an internal combustion engine or the like and an improvement in the precision thereof.
Conventionally, it has been well known that the temperature of the tip of a glow plug used in an internal combustion engine such as a diesel engine is an element that is important as a parameter for controlling the energized state of the glow plug itself.
For this reason, for example, various devices in which a thermocouple is built into the tip portion of the glow plug and which make the temperature of the tip portion directly acquirable and supply the temperature for engine control, and various methods of estimating the temperature of the tip of the glow plug from the resistance value of the glow plug at the time of energization, have been proposed, for example, in JP-A-2001-336468 and etc.
However, in the configuration described above where a thermocouple is disposed in the tip portion of the glow plug to detect the temperature of the tip portion, an adhesive secures the thermocouple, and there is no adhesive whose upper temperature limit is sufficient. In addition, the consistency between the coefficient of thermal expansion of the adhesive and the coefficient of thermal expansion of the thermocouple is not always good. So there are worries that the thermocouple will become disconnected or separate from the place to which it is adhered. And in addition to the problem that the configuration is less than perfect in terms of its solidness, there are also the problems that the configuration of the glow plug itself becomes complicated and expensive.
Further, in conventional methods of estimating the temperature of the tip of the glow plug from the resistance value of the glow plug, the heat transfer environment around the glow plug changes depending on the load and speed of the engine, which in no small way affects the resistance value of the glow plug. So there is the problem that the precision of estimation is not always sufficient.